JPH11174864A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of letter scattering phenomenon and middle missing phenomenon and to enhance display definition by installing means such as a constant voltage power source for impressing a voltage to a charge imparting means and a control means for controlling the constant voltage power source so that the appropriate voltage may be impressed on the charge imparting means in accordance with the thickness of a transferred body. SOLUTION: As for the input of a controller 37 for controlling a laser exposure system copying device, the measurement results from a current monitoring device 38 which is arranged between a constant voltage transformer 36a and a transfer roller 32 and for measuring the current value flowing into the transfer roller 32 are inputted. The thickness of the sheet paper P passing through the transfer roller 32 is judged by the controller 37 in accordance with the current value inputted from the current monitoring device 38. And, the appropriate impressing voltage value is set through a ROM 40 by the controller 37 in accordance with the current value from the device 38, then, the voltage adjuster 36b is controlled by the controller 37, and the voltage impressed by the constant voltage transfer 36a is switched. Thus, the appropriate voltage is impressed on the transfer roller 32 by the constant voltage power source 36.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a transfer device for transferring a toner image formed on a photosensitive drum to a sheet of paper using a contact transfer device in an electrophotographic apparatus or the like.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer, a transfer device for electrostatically or mechanically attracting and transferring a toner image formed on a photosensitive drum onto a sheet of paper is conventionally used as a transfer device. A transfer charger system in which a voltage is applied and electrostatically attracted by a corner discharge is mainly used. However, since there is an advantage in that the amount of ozone generated by corona discharge in recent years is small and the size of the apparatus can be reduced by improving the transfer efficiency, the conductivity to which a voltage is applied by a constant current power supply or a constant voltage power supply is provided. A contact transfer device in which a roller or a conductive brush is brought into contact with the back surface of the sheet paper to apply a transfer charge and perform transfer is also employed.

[0003]

However, in a contact transfer device using a conductive roller or a conductive brush, the following problem has occurred depending on the condition of a power supply to which a voltage is applied. When a constant-current power supply that sets the current to a predetermined value is used, the appropriate transfer current value changes according to the fluctuation of the width of the sheet paper, which is the longitudinal direction of the photosensitive drum. Was needed. Further, in the case of a constant current power supply, as shown in FIG. 15, toner scatters and blurs at the image edge due to a change in resistance of the conductive roller and the conductive brush due to an environmental change, that is, an increase in resistance generated in a low humidity environment. There has been a problem that a visible character dust phenomenon occurs and the display quality deteriorates.

On the other hand, when a constant voltage power supply of a system for setting the voltage to a predetermined value is used, when the thickness of the sheet paper changes like ordinary copy paper and OHP sheet paper, the thickness of the sheet varies depending on the change of the thickness. Therefore, a voltage control corresponding to the change of the appropriate transfer voltage value is required. In addition, since an appropriate transfer voltage value changes in accordance with a change in resistance of the conductive roller or the conductive brush due to an environmental change, voltage control corresponding to the change is necessary. Therefore, even in a constant voltage power supply,
In order to always obtain a good transfer state, control for changing the transfer voltage value according to the thickness of the sheet paper and environmental conditions is required. However, there is no problem that the display quality is deteriorated like the character dust generated by the constant current power supply.

Accordingly, the present invention has been made to solve the above-mentioned problems, and does not cause deterioration in display quality due to generation of character dust when performing transfer with a contact transfer device, and also reduces sheet paper conditions and environmental conditions. The appropriate transfer efficiency can be easily obtained according to
It is an object to provide a highly reliable image forming apparatus capable of improving display quality.

[0006]

According to the present invention, there is provided an image bearing member on which an image is formed in accordance with image information, and a charging means for uniformly charging the image bearing member. An electrostatic latent image forming unit configured to form an electrostatic latent image on the image carrier charged by the charging unit; a developing unit configured to develop the electrostatic latent image to form a developed image; and the image carrier. A charge applying unit that is in contact with the transfer object from the back surface of the transfer object and applies a transfer charge from the back surface of the transfer object; a constant voltage power supply that applies a voltage to the charge application unit; Control means for controlling the constant voltage power supply so as to apply an appropriate voltage to the charge applying means.

According to the present invention, there is provided an image carrier on which an image is formed in accordance with image information, a charging means for uniformly charging the image carrier, and a charging means for solving the above problems. An electrostatic latent image forming unit for forming an electrostatic latent image on the image carrier charged by the developing unit, a developing unit for developing the electrostatic latent image to form a developed image, and a transfer target on the image carrier. A charge applying means for applying a transfer charge from the back side of the transfer receiving body via a constant voltage power supply for applying a voltage to the charge providing means, a thickness detecting means for detecting a thickness of the transfer receiving body, Control means for controlling the constant voltage power supply so as to apply an appropriate voltage to the charge applying means in accordance with a detection result by the thickness detecting means.

According to the present invention, there is provided an image carrier on which an image is formed in accordance with image information, a charging device for uniformly charging the image carrier, and a charging device for solving the above problem. An electrostatic latent image forming unit for forming an electrostatic latent image on the image carrier charged by the developing unit, a developing unit for developing the electrostatic latent image to form a developed image, and a transfer target on the image carrier. Charge applying means for applying a transfer charge from the back side of the object to be transferred, a constant voltage power supply for applying a voltage to the charge applying means, and current detecting means for detecting a current flowing into the charge applying means. A thickness detecting means for detecting a change in current of the current detecting means caused by the transfer object passing through the charge applying means to detect a thickness of the transfer object; and a detection result obtained by the thickness detecting means. A suitable voltage to the charge applying means. It said to applied is intended to provide a control means for controlling the constant voltage power supply.

According to the present invention, there is provided an image bearing member on which an image is formed in accordance with image information, a charging member for uniformly charging the image bearing member, and a charging member for charging the image bearing member. An electrostatic latent image forming unit for forming an electrostatic latent image on the image carrier charged by the developing unit, a developing unit for developing the electrostatic latent image to form a developed image, and a transfer target on the image carrier. Charge applying means for applying transfer charge from the back side of the transfer-receiving body, a constant voltage power supply for applying a voltage to the charge applying means, and current detecting means for detecting a current flowing into the charge applying means. A thickness detecting means for detecting a change in current of the current detecting means which occurs when the transferred body comes into contact with the charge applying means to detect a thickness of the transferred body; The non-image forming portion of the transfer object is It is intended to provide a control means for controlling the constant voltage power supply to apply a proper voltage to the charging unit until passing through the load imparting means.

Further, according to the present invention, there is provided an image bearing member on which an image is formed in accordance with image information, a charging device for uniformly charging the image bearing member, and Electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier, developing means for developing the electrostatic latent image to form a developed image, and Charge applying means for applying a transfer charge from the back surface of the transfer-receiving body, a constant voltage power supply for applying a voltage to the charge applying means, and a current detecting means for detecting a current flowing into the charge applying means. A thickness detection unit that detects a current change of the current detection unit that occurs when the transfer target body comes into contact with the charge applying unit to detect a thickness of the transfer target unit; Storing appropriate applied voltage information to the charge applying means. The storage unit compares the result of detection by the thickness detection unit with appropriate applied voltage information stored in the storage unit, and the non-image forming portion of the transfer object passes through the charge applying unit before the non-image forming unit passes through the charge application unit. Control means for controlling the constant voltage power supply so as to apply an appropriate voltage to the charge applying means.

According to the present invention, in order to realize a contact transfer device which does not pollute the environment and improves transfer efficiency by the above means, when a transfer voltage is applied to a charge applying means by a constant voltage power supply, By applying an appropriate transfer voltage value according to the thickness of the sheet paper, good transfer can be obtained without deteriorating the display quality.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, conditions for realizing the present invention will be described with reference to FIGS. As a charge applying means used when setting each condition, a cylindrical conductive rubber 2 in which a foamable elastomer such as urethane rubber is adhered to an outer periphery of a shaft 1 supported by a guide 5 formed of stainless steel or the like. That is, the transfer roller 3 adjusted to a predetermined resistance value is used. The shaft 2
A stainless steel having an outer diameter of 8 mm (product name: SUS303) is used, and a conductive rubber 2 is formed using a conductive foamable urethane foam so as to have an outer diameter of about 18 mm, and a transfer voltage is applied to the shaft 1. It is designed to be applied. With the above configuration, the resistance between the shaft 1 and the surface of the conductive rubber 2 is about 50 MΩ, and the hardness (ASKER-C) is about 3
The transfer roller 3 is set to 0 °. The characteristics of the transfer roller 3 include the above-described conductivity and flexibility, as well as the fact that the transfer roller 3 is always in contact with the photosensitive drum 4 so that the transfer roller 3 does not contaminate the photosensitive drum 4. There is not.

First, the hardness of the transfer roller 3 and the transfer roller 3
A description will be given of the spring 6 for biasing the spring 6 in the contact direction with the photosensitive drum 4. As a method of urging the transfer roller 3 so as to contact the photosensitive drum 4, a constant load pressing method using a spring 6 and a forced pressing method using a guide roller are generally used. In the forced pressing method using the guide opening, the outer diameter tolerance of the transfer roller 3 is strict, and the transfer roller 3 itself is required to have excessive flexibility.

If the transfer roller 3 is required to have flexibility, it may be necessary to add a mixture of a plasticizer and the like to the transfer roller 3. In this case, the contact point between the photosensitive drum 4 and the transfer roller 3 in the copying apparatus is required. In this case, the plasticizer may be stained from the transfer roller 3 to contaminate the photosensitive drum 4. Considering these facts, it can be said that the constant load pressing method using a spring is superior.

Next, the load of the spring 6 was determined in consideration of the following points. In the contact transfer device using the transfer roller 3, depending on the selection conditions of the hardness of the transfer roller 3 and the load of the spring 6, a so-called hollow phenomenon occurs in which the toner in the central part of the character comes off as shown in FIG. The hollow phenomenon is prominent when relatively thick sheet paper such as a postcard or an OHP sheet is used. Therefore, the hardness of the conductive rubber 2 of the transfer roller 3 is set to 25 °, 30 °, 35 ° (all hardness is ASKER
-C hardness), and the load of the spring 6 is set to 0.010N to 0.
The state of occurrence of the hollowing-out phenomenon when the temperature was changed from 051 N (100 g · f to 500 g · f) was confirmed. The transfer voltage was +1.0 kV using a constant current power supply.
The paper was 80 g / m ² and A3 size.

The results are shown in Table 1. Transfer roller 3 hardness 3
In the case of 5 °, no hollowing out occurred only under the condition of a load of 0.020 N (200 g · f).
In the case of ゜ and 30 ゜, if 0.041 N or less, no generation occurred. From this result, it was confirmed that when the hardness of the transfer roller 3 was 30 ° or less, the load condition under which the hollow phenomenon did not occur was widened.

[0017]

[Table 1]

Next, as a bad effect when the load of the spring 6 is reduced, it is conceivable that transferability is deteriorated (transfer efficiency is lowered). FIG.
Indicates that the transfer roller 3 has a hardness of 25 ° and 30 ° and the load of the spring 6 is 0.020 N to 0.041 N (200 g · f to 40 N).
5 is a graph showing a change in transfer efficiency when the transfer efficiency is set to 0 g · f). (Transfer voltage, paper, etc. are the same as above.) For transfer efficiency, power was forced to 0F during printing of the front solid image.
F, the transfer residual toner on the photosensitive drum was collected with a tape, and calculated by the following method.

Transfer efficiency (%) = (Reflectivity of tape) − (Transfer residual taping reflectivity) (Equation 1) When the numerical value obtained from the above equation 1 is 25% or less, the transferability is at a satisfactory level. It was determined. FIG. 5 shows that the spring load is 0.020 N (200 g · f) regardless of the hardness of the transfer roller 3.
If the value is less than the range, the transferability is poor, and the appropriate range of the spring load is 0.020 N to 0.041 N (200 g · f to 400 N).
g · f). Therefore, the load of the spring 6 is set to 0.031 N (300 g · f) within an appropriate range.

Regarding the hardness of the transfer roller 3, it is determined that a distortion state due to contact with the photosensitive drum 4 is finally determined, and a roller having a smaller amount of distortion is selected. FIG.
The graph shows changes in the distortion rate when two types of transfer rollers having a hardness of 25 ° and 30 ° are brought into contact with the photosensitive drum 4 so as to bite each other by 1.0 mm, and are left under an environmental condition of 50 ° C. The distortion rate was calculated by the following method. Outer diameter = 18m
m, bite amount = 1.0 mm.

[0021]

(Equation 1) It can be seen from FIG. 6 that the distortion rate of the transfer roller having a hardness of 25 ° becomes worse as the standing time becomes longer. From this result, it is assumed that a transfer roller having a hardness of 30 ° that is less likely to cause transfer failure due to distortion when the photosensitive drum 4 is left in contact with the photosensitive drum 4 is used.

Next, an appropriate range of the resistance value of the transfer roller 3 will be described. When the appropriate conditions for applying the voltage to the transfer roller 3 were confirmed for each of the constant voltage power supply and the constant current power supply, in the case of the constant voltage power supply, when the resistance value was 10 ⁶ Ω or less, the half-tone In the image memory, an afterimage of a solid black band appears, and the resistance value is 10
^If it is ¹⁰ Ω or more, the character dust level deteriorates. On the other hand, in the case of the constant current power supply, the image memory has the same resistance value as the constant voltage power supply of 10
⁶ Omega but is generated in the following, the characters dust generation resistance of 10 ⁹
Ω or more, and it was confirmed that the appropriate range was narrower by one order than the constant voltage power supply.

From the above results, it was confirmed that the proper range of the transfer opening-to-roller resistance value was 10 ⁷ Ω to 10 ⁸ Ω as shown in Table 2.

[0024]

[Table 2]

Next, the transfer bias was examined. Regarding the transfer bias, the transferability was examined for two types of transfer bias: (1) transfer bias using a constant voltage power supply and (2) transfer bias using a constant current power supply. The transferability was confirmed in the same manner as in the above-mentioned method, and a reflectance of 25% or less was regarded as a favorable level. Further, regarding the sheet paper, the size and thickness were variously changed, and the change in transferability was confirmed. Table 3 shows an appropriate range of the transfer voltage applied by the constant voltage power supply in a room temperature environment, and Table 4 shows an appropriate range of the transfer current applied by the constant current power supply.

[0026]

[Table 3]

[0027]

[Table 4]

For sheet paper, the sizes are A3, A4-
R (A4 vertical), A5-R (A5 vertical), postcard, thickness 8
0 g / m ^2, and a ^{127g / m 2, 157g / m} 2.
The constant voltage power supply has an applied voltage of 0.8 kV to 2.4 kV,
With a constant current power supply, the applied current was set to 10 μA to 26 μA, and an appropriate transfer area was confirmed under each application condition. From Table 3, it can be seen that, with the constant voltage power supply, even within the same size, the appropriate transfer voltage changes due to the change in the thickness of the sheet paper. For example, A3 size is 80
for proper transfer range of g / m ² paper is 1.0KV～1.4KV, in 127 g / m ² paper 1.8kV~2.2k
V to 80 g / m ² paper and 127 g / m ²
There is no transfer voltage that satisfies both papers with a constant voltage power supply. In addition, when the constant voltage power supply includes that the appropriate transfer voltage slightly changes depending on the size of the sheet paper, it is easy to cause a problem that the transfer efficiency is reduced at a specific size / thickness of the sheet paper. Is guessed.

Next, characteristics of application with a constant current power supply will be described. From Table 4, it can be seen that with the constant current power supply, the appropriate transfer current changes depending on the size of the sheet paper. Specifically, the appropriate transfer current is 14 μA for the A3 size, 16 μA for the A4-R size, 18 μA for the A5-R size, and 20 μA for the postcard size. Although it increases, when the thickness is different within the same size, the appropriate transfer current value does not change much. That is, in the case of the constant current power supply, it is shown that good transfer efficiency can be obtained by appropriately changing the transfer current value depending on the paper size.

The above results are briefly summarized as follows.

(1) In a constant voltage power supply, an appropriate transfer voltage value shifts depending on the thickness of a sheet of paper.

(2) In a constant current power supply, an appropriate transfer current value shifts according to the width of a sheet.

Next, the material of the transfer roller 3 was examined. FIGS. 8 and 9 show the results of confirming the change in the resistance value of the transfer roller 3 depending on the energization time in the case of the ionic conduction type and the case of the ion + electron conduction type. From FIG. 8, in the ionic conduction providing method, the resistance value increases with the increase in the power-on time, and the resistance value increases to 10 ⁹ Ω in a low-temperature and low-humidity environment when the power-on time is equivalent to 96K sheets.

On the other hand, as shown in FIG. 9, in the ion + electron conductivity providing method, the amount of change in resistance is small, and does not reach 10 ⁹ Ω even in the power supply time corresponding to 96K sheets. It has been confirmed from the above examination results that when the resistance value of the transfer roller 3 is 10 ⁹ Ω or more, the level of character dust deteriorates and image quality deteriorates. An electronic conductivity imparting method was used.

Based on the above results, first, a constant current power supply was used as a transfer power supply, and an ion + electron conductivity provision method was used as a roller conduction provision method, and a life test by continuous paper passing was performed at an appropriate transfer current. However, in the case of passing 80K sheets, there is a problem that the character dust level is deteriorated in a low-temperature and low-humidity environment, and image quality is impaired. From the results of the examination of the material of the transfer roller 3 described above, it has been confirmed that the character dust deteriorates when the resistance value of the transfer roller 3 is 10 ⁹ Ω or more, and this result does not apply. Therefore, the resistance value of the transfer port 3 was again changed finely to confirm the fluctuation of the character dust level.

As a result, as shown in FIG. 10, it was confirmed that the resistance value of the transfer roller 3 was 8.5 × 10 ⁸ Ω or less in a favorable range of the character dust level.

Next, there is a possibility that the variation in the resistance value of the transfer roller 3 affects the character dust, and the measurement was actually performed to confirm the authenticity. 5mm x 5mm for resistance measurement
The current value actually applied was applied by using the microelectrode of No. 3 and confirmed. Table 5 shows the results. In the ion + electron conductivity providing method used in this study, it was confirmed that the resistance value ± 3.0 times varied in the longitudinal direction of the transfer roller 3.

[0038]

[Table 5]

Next, the influence of the variation in the resistance value on the character dust was confirmed. As a result, as shown in FIG.
In a low-temperature and low-humidity environment, considering the variation in the resistance value, it can be seen that character dust occurs at the equivalent of 76K sheets.
It has been confirmed that even when a transfer roller using the ion + electron conductivity imparting method is used, the deterioration of character dust cannot be prevented with a constant current power supply.

From the above results, it was confirmed that a constant voltage power supply was advantageous as a power supply used for applying the transfer roller 3. However, as described above, with the constant voltage power supply, an appropriate transfer voltage value depends on the thickness of the sheet paper. It has been confirmed that it changes.
In order to correct this, it is necessary to detect the thickness of the sheet paper and correct the applied voltage value.

In the present invention, therefore, a voltage is applied to the transfer roller 3 by using a constant voltage power supply, and is applied at an appropriate applied voltage value in accordance with the thickness of the sheet paper to obtain good transfer. It is.

Next, the present invention will be described with reference to the embodiment shown in FIGS. 12 to 14 which uses a transfer apparatus which satisfies the conditions discussed above. A document glass 8a on which a document O is mounted is disposed above a main body 8 of a laser exposure type copying apparatus 7 which is an image forming apparatus, and is covered with a document cover 8b. An illumination lamp 9a, a mirror 9b, and a condenser lens 9 for reading image information of the original O are provided below the original glass 8a.
A reading device 9 having a c is disposed. A rotatable photosensitive drum 10 is provided substantially at the center of the main body 8.
An image corresponding to the image information recorded by the laser exposure device 11 that converts the image information read by the reading device 9 into a laser beam is formed on the surface of the photosensitive drum 10. Around the photoreceptor drum 10, the photoreceptor drum 10 is composed of a corona wire 12a and a grid screen 12b along the direction of rotation, and is uniformly about -630.
A charging device 12 for charging to V, an exposure position 11 a of the laser exposure device 11, and the photosensitive drum 1 by the laser exposure device 11.
Developing device 1 that supplies toner to the electrostatic latent image formed in image forming unit 0
4. A transfer device 16 for transferring the toner image formed on the photosensitive drum 10 by the developing device 14 to a sheet paper P as a transfer-receiving member, and a chest for scraping off the toner remaining on the surface of the photosensitive drum 10 after the transfer is completed. And a static eliminator 20 for eliminating charges remaining on the surface of the photoreceptor drum 10.

Here, about -650 is applied to the corona wire 12a.
A bias voltage of V is applied. Laser exposure device 11
Gives convergence to a laser beam generated from a semiconductor laser element (not shown), converts the laser beam into a laser beam having a substantially circular cross-sectional shape, and then converts the converted laser beam along the axial direction of the photosensitive drum 10. Deflecting device 11b for deflecting the laser beam, a laser beam deflected by the laser deflecting device 11b, and the deflection angle of the laser beam and the optical axis on the photosensitive drum 10 in order to sequentially form an image on the exposure position 11a of the photosensitive drum 10. Imaging lens 11c, imaging lens 11c for matching the distance from to the position where the beam is imaged
A mirror 11d for guiding the laser beam passed through to the exposure position 11a of the photosensitive drum 10, and a dustproof glass 11e for dustproofing the mirror 11d.

The developing device 14 is a conventionally known magnetic brush type developing device for performing development using a two-component developer composed of toner and carrier, and has a housing 14a for accommodating the two-component developer. A developing roller 17 around which a magnetic brush is formed during rotation is provided.

The cleaning device 18 comprises a cleaning blade 18a and an auger 18b for moving the toner scraped off by the cleaning blade 18a in the direction of the rotation axis of the photosensitive drum 10. The toner collected by the cleaning device 18 is collected by a toner collection device (not shown), and is collected and replaced with a new one each time the toner reaches a predetermined amount.

In the lower portion of the main body 8, the sheet paper P taken out of the paper feed cassette device 22 integrated with the manual feed tray 22 a by the pickup roller 21 is transferred to the photosensitive drum 10.
There is provided a sheet paper transport path 24 that leads to the paper output tray 23 through the space between the transfer device 16 and the transfer device 16. Upstream of the photoconductor drum 10 in the sheet paper conveyance path 24, separation conveyance rollers 26,
The inclination of the sheet P with respect to the transport direction is corrected, and the leading end of the toner image on the photosensitive drum 10 and the sheet P
A pair of aligning rollers 27 that align the leading ends and feed the sheet paper P at the same speed as the moving speed of the outer peripheral surface of the photosensitive drum 10 are arranged. A fixing roller 30 for heating / pressing and fixing a toner image on paper P and a paper discharge roller 31 are arranged.

Next, the transfer device 16 will be described in detail. It is a charge applying means of the transfer device 16 and has a spring load of 0.031 N
The transfer roller 32 urged toward the photosensitive drum 10 by the spring 33 set to (300 g · f) is brought into contact with the transfer roller 32. The transfer roller 32 is formed of a foamed urethane foam around a shaft 32 a made of stainless steel (SUS303) and having an outer diameter of 8 mm. A conductive rubber roller 32b having an outer diameter of 18 mm is adhered, and the resistance between the shaft 32a and the surface of the conductive rubber roller 32b is set to about 50 MΩ, and the hardness (ASKER-C) is set to about 30 °.

The transfer roller 32 is a conductive rubber roller 3
2b is rotated by a gear (not shown) for transmitting the rotation of the photosensitive drum 10 so that the surface speed becomes equal to the peripheral speed of the photosensitive drum 10.

Reference numeral 34 denotes a sheet paper P by a constant voltage power supply 36 including a constant voltage transformer 36a and a voltage variable unit 36b.
Is a voltage control mechanism for applying an appropriate transfer voltage according to the thickness of the transfer roller 32 to the shaft 32a of the transfer roller 32.
Installed between the constant voltage transformer 36a and the transfer roller 32,
A measurement result from a current monitoring device 38 for measuring a current value flowing into the transfer roller 32 is input.

The controller 37 determines the thickness of the sheet P passing through the transfer roller 32 according to the current value input from the current monitor 38 as shown in FIG. That is, when the applied voltage is 1.0 kV, the current value is 25.
If the current value is 15.0 to 20.0 μA, the sheet thickness is 80 g / m ² ,
If it is 8.0 to 10.0 μA, the paper thickness is 127 g / m ² ,
If it is 3.0 to 5.0 μA, it is determined that the paper thickness is 157 g / m ² . On the other hand, the environmental conditions were changed from a high temperature and high humidity of 30 ° C. and 85% RH to a low temperature and low humidity of 10 ° C. and 20% RH. Inspection was performed every time, and the results as shown in Tables 6, 7, and 8 were obtained. From this result, although the appropriate transfer voltage value changes depending on the change in the environmental conditions, the change amount is small and a sufficiently good transfer can be obtained at the same transfer voltage value as in the warm condition. That is, regardless of changes in environmental conditions,
If the sheet thickness 80 g / m ² proper applied voltage 1.2 kV, a if the paper thickness 127 g / m ² proper applied voltage 1.6 kV, a proper applied voltage 2.0kV if paper thickness 157 g / m ² good Transfer is obtained.

[0051]

[Table 6]

[0052]

[Table 7]

[0053]

[Table 8]

Then, as shown in Table 9, the ROM 40 stores
If the sheet P is not detected, the applied voltage is 1.0 kV and the paper thickness is 8
If it is 0 g / m ² , the proper application voltage is 1.2 kV and the paper thickness is 12
If it is 7 g / m ² , the proper application voltage is 1.6 kV and the paper thickness is 15
If it is 7 g / m ² , an appropriate applied voltage value of 2.0 kV for the transfer roller 32 corresponding to each paper thickness is stored.

[0055]

[Table 9]

The control device 37 sets an appropriate applied voltage value from the ROM 40 according to the current value from the current monitor device 38, controls the voltage variable device 36b, and switches the applied voltage by the constant voltage transformer 36a. . As a result, the constant voltage power supply 36 applies a predetermined appropriate application voltage corresponding to the sheet pressure of the sheet paper P to the shaft 32a.

The applied voltage when the sheet P is not detected is set to 1.0 kV, which is the value at which the change in the inflow current when the sheet P contacts the transfer roller 32 is most easily observed. Further, the elapsed time including the rise time of the constant voltage transformer 36a from the contact of the sheet P with the transfer roller 32 to the switching of the applied voltage by the constant voltage power supply 36 is as shown in FIG. (However, the printing speed of the laser exposure type copying apparatus 7 is set to 125 mm / S.) As a result, the monitoring time of the change in the current value by the current monitoring device 38 when the sheet paper P contacts the transfer roller 32 is 0.01 second. , Control device 37
Time for selecting an appropriate applied voltage of the ROM 40 by 0.01 seconds,
The time from the change of the constant voltage transformer 36a by the voltage variable device 36b to the stabilization of the constant voltage transformer 36a is 0.01 seconds,
It takes 0.03 seconds in total. Printing speed is 125mm / S
Therefore, an area from the leading end of the sheet paper P to about 4.0 mm is an appropriate application voltage adjustment area.

Next, the operation will be described. When the printing operation is started, the photosensitive drum 10 is rotated in the direction of arrow s at a speed of 125 mm / sec.
Is uniformly charged to about -630 V by the exposure position 11a
Then, the irradiation of the laser exposure device 11 forms an electrostatic latent image corresponding to the image information of the document O. Next, toner is applied to the electrostatic latent image on the photosensitive drum 10 by a developing roller 17 to which a bias voltage of −400 V is applied by a developing device 14, a toner image is formed, and the toner image reaches the transfer device 16.

On the other hand, in the sheet cassette device 22,
Sheet paper P having a predetermined thickness is picked up by a pickup roller 21, separated one by one by a separation conveyance roller 26, sent to an aligning roller 27, aligned with a toner image on the photosensitive drum 10, and transferred to a transfer device 16. Sent. Prior to the arrival of the sheet P, a voltage of 1.0 kV is applied to the transfer roller 32 by the constant voltage power supply 36, and the current monitoring device 38 outputs a current value of 25.0 μA at which the sheet P is not detected.
Is detected and input to the control device 37. Thereafter, when the sheet paper P comes into contact with the transfer roller 32, the current value of the current monitoring device 38 varies according to the thickness of the sheet paper P. Accordingly, the control device 37 determines the thickness of the sheet paper P, selects an appropriate application voltage value according to the thickness from the ROM 40 storing the appropriate application voltage values shown in Table 9, and controls the pressure transformer 36b. An appropriate voltage is applied to the shaft 32a by the constant voltage transformer 36a.

[0060] That is, the thickness of the sheet paper P 80 g / m ² in 1.2 kV, the thickness 127 g / m ² paper sheet P 1.
6 kV, 2.0 k at 157 g / m ² thickness of sheet paper P
V is applied to the shaft 32a. Note that the switching time from the contact of the sheet paper P to the transfer roller 32 to the application of the appropriate voltage by the constant voltage power supply 36 is about 0.03 seconds, and the switching time is about 4 mm. Since the switching is performed, the voltage switching operation is reliably performed before the image area of the sheet paper P reaches the transfer roller 32. Therefore, the image area of the sheet paper P to which the toner image is transferred is provided with the transfer charge by the switched proper transfer voltage while passing through the contact nib between the photosensitive drum 10 and the transfer roller 32, and The toner image on the body drum 10 is transferred well.

Thereafter, the toner transferred to the sheet paper P is separated from the surface of the photoreceptor drum 10 together with the sheet paper P, is conveyed to the fixing roller 30 by the conveyor belt 28, and is discharged via the discharge roller 31. The paper is discharged to the paper tray 23. During this time, the sheet paper P passes through the transfer roller 32, and the current monitor device 38 detects that fact, and the control device 3
7 recognizes that, controls the pressurizing transformer 36b,
The voltage applied to the shaft 32a by the constant voltage transformer 36a is returned to 1.0 kV. After the transfer of the toner image onto the sheet paper P, the photosensitive drum 10 continues to rotate, and after the remaining toner is removed by the cleaning device 18, the charge removal device 2
By 0, the residual charge is eliminated, and the next image can be formed. As described above, in the transfer device 16, a series of image forming steps are repeated while switching an appropriate application voltage to the transfer roller 32 by the constant voltage power supply 36 according to the thickness of the sheet paper P.

With such a configuration, when a transfer voltage is applied by the constant voltage power supply 36 to the transfer roller 32 that performs transfer by contacting the photosensitive drum 10 via the sheet paper P,
By applying an appropriate voltage value in accordance with the thickness of the sheet paper P, regardless of the type of sheet paper P and the environmental conditions, it is possible to obtain good transfer efficiency without generating character dust and white spots and always perform good transfer. The display quality of an image can be improved. Moreover, the thickness of the sheet paper P can be reduced without using a precise and expensive detecting device.
By detecting a change in the current of the transfer roller 32 caused by the contact of the sheet paper P with the transfer roller 32, it can be easily identified, and by selecting an appropriate applied voltage value from the information stored in the ROM 40 in response to the change. The control device 37 allows the constant voltage power supply 36 to be easily controlled. Further, the detection of the thickness of the sheet P and the switching of the applied voltage value by the constant voltage power supply 36 are performed between the time when the leading end of the sheet P contacts the transfer roller 32 and the time when the image area of the sheet P reaches the transfer roller 32. When the image area reaches the transfer roller 32, an appropriate transfer voltage value is reliably applied to the transfer roller 32, and good transfer can be obtained over the entire image area.

It should be noted that the present invention is not limited to the above-described embodiment, but can be changed without departing from the spirit thereof. For example, the charge applying means is brought into contact with the image carrier at the transfer position. A transfer brush in which a transfer voltage is applied to the conductive brush by a constant voltage power supply may be used.
Any material having conductivity and capable of imparting charge to the toner image on the image carrier is optional, such as its material and outer diameter resistance value. The appropriate applied voltage value also depends on the resistance value of the charge imparting means. Is set. Further, the size, thickness, and the like of the transfer object used in the image forming apparatus are optional as needed.

[0064]

As described above, according to the present invention, when the transfer is performed by the contact transfer means having good transfer efficiency and capable of preventing environmental pollution, it depends on the thickness of the transfer object on which the toner image is transferred. By properly setting the transfer voltage applied to the charge applying means by the constant voltage power supply, regardless of the type of the transfer object and the environmental conditions, the image quality is always stable without causing a decrease in image quality due to character dust or white spots. Good transferability can be obtained, and good images can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a transfer roller used when setting conditions for realizing the present invention.

FIG. 2 is a longitudinal side view showing a transfer roller used when setting conditions for realizing the present invention.

FIG. 3 is a side view in the shaft direction showing a transfer roller used when setting conditions for realizing the present invention.

FIG. 4 is an explanatory diagram showing a hollow phenomenon that occurs when setting conditions for realizing the present invention.

FIG. 5 is a graph showing a change in transfer efficiency due to a change in a spring load of a transfer roller used when setting conditions for realizing the present invention.

FIG. 6 is a graph showing a change with time of a distortion rate of a transfer roller used when setting conditions for realizing the present invention.

FIG. 7 is an explanatory diagram showing an image memory phenomenon that occurs when setting conditions for realizing the present invention.

FIG. 8 is a graph showing a time-dependent change in the resistance value of the transfer roller in the ionic conductivity providing method used when setting conditions for realizing the present invention.

FIG. 9 is a graph showing the time-dependent change of the resistance value of the transfer roller in the ion + electron conductivity providing method used when setting the conditions for realizing the present invention.

FIG. 10 is a graph showing the occurrence of character dust with respect to the resistance value of a transfer roller used when setting conditions for realizing the present invention.

FIG. 11 is a diagram illustrating a time-dependent change in the resistance value including a variation in the ion + electron conduction application method of the transfer roller used when setting the conditions for realizing the present invention, and a generation state of character dust with respect to the change in the resistance value. It is a graph.

FIG. 12 is a configuration diagram illustrating a laser exposure type copying apparatus according to an embodiment of the present invention.

FIG. 13 is a block diagram illustrating a voltage control mechanism that applies an appropriate transfer voltage to the transfer roller according to the embodiment of the present invention.

FIG. 14 is a graph showing a time required for switching an appropriate transfer voltage according to the embodiment of the present invention.

FIG. 15 is an explanatory diagram showing a character dust phenomenon that has occurred in a conventional device.

[Explanation of symbols]

 7 ... Laser exposure type copying apparatus 8 ... Main body 10 ... Photoconductor drum 11 ... Laser exposure apparatus 14 ... Developing apparatus 16 ... Transfer apparatus 32 ... Transfer roller 32a ... Shaft 32b ... Conductive rubber roller 33 ... Spring 34 ... Voltage control mechanism 36 ... constant voltage power supply 36a ... constant voltage transformer 36b ... voltage variable device 37 ... control device 38 ... current monitor device 40 ... ROM

Claims (7)

[Claims] An image carrier on which an image is formed in accordance with image information; a charging unit for uniformly charging the image carrier; and an electrostatic latent image on the image carrier charged by the charging unit. Forming an electrostatic latent image, developing means for developing the electrostatic latent image to form a developed image, and transferring the electric charge from the back surface of the transfer object which is in contact with the image carrier via the transfer object Control means for applying a voltage to the charge applying means, and controlling the constant voltage power supply to apply an appropriate voltage to the charge applying means according to the thickness of the transfer object. And an image forming apparatus. 2. An image carrier on which an image is formed in accordance with image information, a charging means for uniformly charging the image carrier, and an electrostatic latent image on the image carrier charged by the charging means. Forming an electrostatic latent image, developing means for developing the electrostatic latent image to form a developed image, and transferring the electric charge from the back surface of the transfer object which is in contact with the image carrier via the transfer object , A constant voltage power supply for applying a voltage to the charge applying unit, a thickness detecting unit for detecting the thickness of the transfer object, and the charge applying unit according to a detection result by the thickness detecting unit. A control unit for controlling the constant voltage power supply so as to apply an appropriate voltage to the image forming apparatus. 3. An image carrier on which an image is formed in accordance with image information, charging means for uniformly charging the image carrier, and an electrostatic latent image on the image carrier charged by the charging means. Forming an electrostatic latent image, developing means for developing the electrostatic latent image to form a developed image, and transferring the electric charge from the back surface of the transfer object which is in contact with the image carrier via the transfer object , A constant voltage power supply for applying a voltage to the charge applying means, and a current detecting means for detecting a current flowing into the charge applying means, wherein the transfer object passes through the charge applying means. The thickness of the object to be transferred is detected by detecting a change in the current of the current detecting unit caused by the current detection, and an appropriate voltage is applied to the charge applying unit according to the detection result by the thickness detecting unit. Control means for controlling the constant voltage power supply; An image forming apparatus comprising: 4. An image carrier on which an image is formed in accordance with image information, charging means for uniformly charging the image carrier, and an electrostatic latent image on the image carrier charged by the charging means. Forming an electrostatic latent image, developing means for developing the electrostatic latent image to form a developed image, and transferring the electric charge from the back surface of the transfer object which is in contact with the image carrier via the transfer object And a constant voltage power supply for applying a voltage to the charge applying means, and a current detecting means for detecting a current flowing into the charge applying means. A thickness detecting unit that detects a change in the current of the current detecting unit that occurs at the time of contact to detect a thickness of the transfer target body;
Control for controlling the constant voltage power supply so that an appropriate voltage is applied to the charge applying unit before the non-image forming portion of the transfer object passes through the charge applying unit in accordance with the detection result of the thickness detecting unit. And an image forming apparatus. 5. An image carrier on which an image is formed in accordance with image information, charging means for uniformly charging the image carrier, and an electrostatic latent image on the image carrier charged by the charging means. Forming an electrostatic latent image, developing means for developing the electrostatic latent image to form a developed image, and transferring the electric charge from the back surface of the transfer object which is in contact with the image carrier via the transfer object And a constant voltage power supply for applying a voltage to the charge applying means, and a current detecting means for detecting a current flowing into the charge applying means. A thickness detecting unit that detects a change in the current of the current detecting unit that occurs at the time of contact to detect a thickness of the transfer target body;
A storage unit for storing appropriate applied voltage information to the charge applying unit according to the thickness of the transfer object, and comparing a detection result by the thickness detecting unit with appropriate applied voltage information stored in the storage unit. Controlling means for controlling the constant voltage power supply so as to apply an appropriate voltage to the charge applying means until the non-image forming portion of the transfer object passes through the charge applying means. Image forming apparatus. 6. The transfer roller according to claim 1, wherein the charge applying means is a transfer roller having a flexible conductive roller attached around a conductive shaft. Image forming device. 7. The constant voltage power supply according to claim 1, wherein the control means controls the constant voltage power supply so as to increase an appropriate voltage applied to the charge applying means when the thickness of the transfer object increases. An image forming apparatus according to claim 1.